<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
        <script type="text/javascript">
            var c = 0;
            var t;
            function timedCount() {
                document.getElementById('txt').value = c;
                c = c + 1;
                t = setTimeout("timedCount()", 1000);
            }
            function stopCount() {
                c = 0;
                setTimeout("document.getElementById('txt').value=0", 0);
                clearTimeout(t);
            }
        </script>
    </head>
    <body>
        <form>
            <input type="button" value="开始计时！" onClick="timedCount()">
            <input type="text" id="txt">
            <input type="button" value="停止计时！" onClick="stopCount()">
        </form>
        <p>请点击上面的“开始计时”按钮来启动计时器。输入框会一直进行计时，从 0 开始。点击“停止计时”按钮可以终止计时，并将计数重置为 0。</p>
    </body>
</html>
